[Dovecot] Postfix Virtual Users and Directory Permissions

[Michael Starks]

I have followed the instruction here: 
http://www.postfix.org/VIRTUAL_README.html#virtual_mailbox

There are five virtual domains configured and each directory containing 
each domain is owned by one UID/UID with permissions of 700.  I can send 
mail to each domain and it is stored in the appropriate Maildir under 
the correct directory.  The system is OpenBSD 3.8 STABLE.  So far, so good.

Now comes Dovecot.  What I would like to do is to have one set of 
credentials for 4 of the domains, and another for the remaining.  I 
would also like to *not* use a database backend for authentication at 
this time and would prefer to stick with standard UNIX /etc/passwd and 
/etc/shadow.

Considering the directories are all owned by one user, does Dovecot need 
to be configured to use the same user as auth_userdb = static?  That 
would make sense.

What I'm not clear on is how Dovecot would know which domains are 
associated with which user, and does the user need permissions to those 
directories or is that handled by impersonation?

Thanks in advance.